1. Field
Example embodiments disclosed herein relate in general to the field of wavelength division multiplexing and more particularly to a multifunctional and reconfigurable Dense Wavelength Division Multiplexing (DWDM) optical node. Example embodiments disclosed herein also relate to an optical node and an optical network including a reconfigurable optical add drop multiplexer core device.
2. Related Art
Wavelength Division Multiplexing (WDM) and Dense Wavelength Division Multiplexing (DWDM) are technologies that enable a multitude of optical wavelengths of differing frequencies to be transported over a single optical fiber. A DWDM network is constructed by interconnecting multiple DWDM network elements. Each network element typically includes, for example, optical multiplexing equipment, optical de-multiplexing equipment, optical amplifiers, optical power monitors, optical supervisory channel processors, network element control processors, and optical converters.
First generation DWDM network equipment provided the ability to transport a multitude of optical wavelengths between two points over a single pair of optical fibers. These systems are referred to as DWDM point-to-point systems. Second generation DWDM network equipment provided the ability to interconnect DWDM network elements in a “ring” configuration. These elements included two DWDM network interfaces and multiple single wavelength ports used to add and drop wavelengths to and from the DWDM network interfaces. Second generation DWDM network elements provided the ability to “pass” wavelengths directly between their two DWDM network interfaces. However, in order to do this, fiber cables had to be manually interconnected within a system each time a “pass-through” connection was required.
Third generation DWDM network elements included Reconfigurable Optical Add Drop Multiplexers, referred to as ROADMs. ROADMs provided the ability to remotely reconfigure the DWDM network element. For these systems, wavelengths could be remotely configured to pass through the network element without manual intervention. Since these “third generation” DWDM network elements also included only two DWDM network interfaces, they are referred to as 2-degree network elements. But these “third generation” DWDM network elements connect only a single add-on device to the ROADMs. As a result, while they are reconfigurable, they are not multifunctional, which limits their usefulness.
In addition, these third generation ROADMs may be part of a network that experiences fiber four-wave mixing (FWM), which plagues many networks that transmit an optical signal having three or more wavelengths over a single optical fiber. FWM is the dominant non-linear penalty for non-SMF-28 fiber types, such as TrueWave Classic (TW-C), TrueWave Plus (TW+), TrueWave Reduced Slope (TW-RS) and Large Effective Area Fiber (LEAF). It is caused by non-linearities in the optical fiber over which the optical signal is transmitted. FWM generates deleterious cross-talk products that vary in power and wavelength, depending on system parameters such as fiber slope, fiber zero dispersion wavelength, optical launch power, channel spacing and the number of spans. FWM occurs in optical fibers with non-linear transmission characteristics when three optical signals of different wavelengths are carried on the optical fiber. These non-linearities generate a fourth optical signal from the three original signals, which is called a cross product, a cross-talk product, or a mixing product, that decreases the signal-to-noise ratio of the three original optical signals. If more than three wavelengths are transmitted on the same optical fiber with non-linear transmission characteristics, more than one additional optical signal is generated. The number of additional generated optical signals is equal to the number of possible combinations of three wavelengths from among the total number of wavelengths transmitted on the optical fiber. As a result, FWM increases as the number of transmitted wavelengths increases.
The presence of FWM cross products affects a network in at least two ways. First, the optical power of the generated cross products depletes the optical power of the optical signals transmitted on the network that carry information, and therefore FWM cross products affect channel OSNR (optical signal-to-noise ratio), resulting in a larger than normal power loss over the span of a fiber optic cable. Second, cross products of exactly the same wavelength as optical signals carrying information on the network create coherent interference/crosstalk and produce a significant OSNR margin reduction, which can lead to traffic outages.
Thus, it is useful to have a fourth generation DWDM optical node that is multifunctional in addition to being reconfigurable. In addition, it is useful to have a multifunctional and reconfigurable DWDM node employing a ROADM connected to more than one add-on device to provide multifunctionality. Further, it is useful to have an optical network including a plurality of such optical nodes. In addition, it is also useful to configure both third and fourth generation DWDM network elements, such as ROADMs to reduce any FWM that is generated from the transmission of at least three wavelengths on a single optical fiber in a network to which the third and fourth generation ROADMs belong.